Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$182.76	3.419%	$189.0086	$189.01	$189.00	$189.00
Purchase #2	$135.50	12.182%	$152.0066	$152.01	$152.00	$152.00
Purchase #3	$37.47	7.729%	$40.3661	$40.37	$40.35	$40.40
Purchase #4	$228.32	11.256%	$254.0197	$254.02	$254.00	$254.00
Purchase #5	$167.46	8.691%	$182.0139	$182.01	$182.00	$182.00
Purchase #6	$247.43	3.707%	$256.6022	$256.60	$256.60	$256.60
Purchase #7	$223.42	6.213%	$237.3011	$237.30	$237.30	$237.30
7 purchase totals =	$1,222.36		$1,311.3182	$1,311.32	$1,311.25	$1,311.30